Glass composition and method



Aug. 11, 1970 KESHARl ET AL GLASS COMPOSITION AND METHOD 2 Sheets-Sheet1 Filed Nov. 15, 1965 ATTORA/EXI United States Patent 3,523,779 GLASSCOMPOSITION AND METHOD Hossein R. Keshari and William F. Mahoney,Toledo, Ohio, assignors to Owens-Illinois, Inc., a corporation of OhioFiled Nov. 15, 1965, Ser. No. 507,952 Int. Cl. C03c 3/24 US. Cl. 65134 8Claims ABSTRACT OF THE DISCLOSURE A soda-lime frit glass compositioncontaining chromium and cobalt in proportioned amounts on an oxide basisranging between about a maximum of 1.5-2.2 weight percent total chromeoxide calculated as Cr O about 0.3-0.6 weight percent hexavalent chromeoxide calculated as CrO the amount of trivalent chrome oxide beingadjusted to accommodate the amount of hexavalent chrome oxide, and fromabout 2.2-3.0 weight percent of oxides of cobalt, and a method ofproducing soda-lime possessing enhanced properties of absorbency tolight in the shortwave visible and ultraviolet regions of the spectrumincluding dissolving in a molten mass of slightly oxidized soda-limeglass chromium and cobalt constituents in amounts producing a resultantsoda-lime glass possessing an oxide composition, including 0.003-001 CrOand 0.03-0.06 total chromium as Cr O and 0.030.l percent by weight ofoxides of cobalt.

This invention relates to the manufacture of colored glasses; moreparticularly, the invention relates to highly colorant enriched bluefrit glass batch compositions, and to the vitreous composition madetherefrom. Also, the invention relates to a method of manufacturing bluecomposite glasses using said blue frit glasses of the in vention.

In conventional operations for producing colored glasses, one of thevery substantial problems encountered is in changing a glass meltingtank over from one color to another, or from a colorless to a coloredglass making operation.

The problem arises from the fact that, for example, the first colorcomposition must be dumped and the tank refilled with a second colorcomposition. Usually the tank change is so scheduled as to permitproduct run-out over as large a portion of the transition as possible.However, there is an intermediate interval of one to three daysduration, wherein the prior color tails out and the new color begins, inwhich the glass composition is in transition and as such must be dumped.This transition glass is off-color and unsuited for commercialutilization. Considering the fact that glass melting tanks hold up to100 tons of melt or more, it will be understood that the transitioncaused by dumping is very expensive.

This, of course, brings to mind an ideal situation where a colorlessbase glass composition would be used in the tank and colorant, asdesired is added at the forehearth to fulfill specific end-colorrequirements. By so operating, the conditions of firing of the tank andthe feeding of batch ingredients into the tank would all becomesubstantially fixed factors. Careful adjustment and stabilization oftank conditions would lead to the production of 3,523,770 Patented Aug.11, 1970 ice high quality products. The tank conditions, oncestabilized, would remain so and variables would be avoided.

Such a forehearth coloring method has important ad vantages over thetank method for producing colored glass, in which the colorant materialis added to the base glass batch and introduced directly into themelting and refining tank. Thus, by the forehearth method, as manycolors can be produced simultaneously as there are forehearthsassociated with the melting furnace.

Further, in a given forehearth, a transition from one color to anothercan be made in a matter of one to three hours, as contrasted to a matterof one to three days to change a tank from one color to another.

Also, if desired, both clear and colored glassware can be madesimultaneously from the same melting tank, by using differentforehearths, and adding colorant frit glass to some, and running theclear base glass through others.

In manufacturing the blue glass by techniques of the present invention,it is desirable to achieve high pulls, or production rates, from aselected forehearth or forehearths utlizing the invention. This may beachieved up to tons per operating day under the one modification hereindisclosed.

Further, smaller quantities of colorant material are required by theforehearth coloring method than by the known melting-tank practice wherethe colorant is incorporated into the tank batch and melted withsubstantial losses of volatile colorant material during the extendedmelting and refining operation.

Additionally, the manufacture of deep blue glasses by conventionalmethods has presented serious economic problems because of inefiicientuse of fuel. These glasses have an absorption band in the near infraredcausing much of the radiant energy of the flames to be absorbed in theupper layer of molten glass. Since commercial melting furnaces aredesigned to accommodate a depth of several feet of molten glass, heattransmission is a serious problem. Since colorless flint glass has ahigh transmission in the near infrared region of the spectrum, thepresent invention permits a substantial reduction in melting costs bypermitting the blue colorants to be added after the melting has beencompleted.

It is well-known in the art that common blue glass compositions exhibitvery little absorption in the ultraviolet region of the spectrum. Thismeans that the contents of ordinary blue glass containers are subject toexposure to ultraviolet and short wave radiation within the visiblespectrum. In the case of comestible products marketed in glasscontainers, the deterioration in taste of beer, wine, ale andorange-flavored soft drinks, the development of rancidity in cookingoils and the loss of vitamin C content in milk have been traced toexposure to the aforesaid short-wave visible and ultraviolet radiation.

It is therefore an object of the present invention to provide a novelblue glass composition that exhibits substantial absorption in theshort-wave radiation of the visible and ultraviolet ranges.

It is another object of the invention to provide a novel colorant fritglass composition that will produce a deep blue color when added to asubstantially colorless base glass.

Another important object is to provide a method of adding the coloredfrit glass to the bulk stream of molten glass while the molten glass isflowing through the forehearth to the forming equipment.

Still another object is to provide a frit glass composition that iscapable of readily admixing with a colorless soda-lime base glass in theforehearth of a conventional furnace so as to permit pull rates of up to40 tons per operating day.

Another object of this invention is to provide a method of producing aglass composition possessing a deep blue coloration Without the heattransfer problems normally associated with the melting and fining ofdeep blue batch materials.

Still a further object of this invention is to provide a colored fritglass composition that is capable of admixing with an essentiallycolorless base glass to form a deep blue color in the aforesaid baseglass through the pres ence of oxides of hexavalent chrome, trivalentchrome, and cobalt in proper combination.

In attaining the objects of this invention, one feature resides in thepreparation of a frit glass containing, in addition to the ordinaryglass forming oxides, sufficient Cr O CrO and C in proper combination toproduce a deep blue coloration. The frit glass should also containsufficient alkali oxides to facilitate the dissolution of Cr O when thefrit glass is subsequently admixed with the base glass.

Another feature resides in admixing the aforesaid frit, under properconditions of agitation, in the forehearth of a commercial glass meltingfurnace, with an essentially colorless soda-lime base glass compositionto produce the desired blue coloration.

The above and other objects, features and advantages of the presentinvention will become apparent to those skilled in the art upon readingthe detailed description contained herein.

FIG. 1 is a longitudinal sectional elevational view, partiallydiagrammatic, of an apparatus which may be used in practicing the methodof the present invention.

FIG. 2 is a graphic representation depicting, by comparison, thetransmittance characteristics of standard Maryland Blue Grass and aglass prepared in accordance with the concepts of the present invention.

The apparatus includes a furnace tank in which the base glass is meltedand refined. A plurality of forehearths such as the depicted forehearth11, may be provided in connection with the tank. The molten glass 9,herein referred to as the base glass, flows from the tank over a dam 31into a channel extending the length of the forehearth. The frit materialwhich is supplied in regulated amounts to the forehearth is dischargedby gravity from a suitable container (not shown) through a spout orspouts 25. The frit during its passage through a melting section of theforehearth is melted and mixed to some extent with base glass. Themixture flows beneath a skimmer block 19. Stirring devices and 21 effectfurther mixing of the glass and colorant constituents, resulting in ahomogeneous glass which is discharged through an outlet 22. Thedischarge of the glass is under the control of a feeder mechanism 24 bywhich measured charges or gobs of glass emanating from the outlet 22 aresevered from the supply body and delivered to the molds of a formingmachine.

The glass which is added to the base glass flowing from the tank 10 issupplied in one form as a solid frit produced by melting the raw batchmaterials, cooling and reducing them to a powdered or granulated fritform, as by introducing the melted raw batch materials directly into abody of water. In its finely particulated form, the frit is absorbed andmelted in the forehearth at a temperature much lower than that requiredfor melting the raw batch forming the base glass.

In another form, the frit may be added in molten state. It is,therefore, contemplated herein that the term frit may include eitherform of the colorant glass material.

The amount of frit entering the forehearth is usually only a smallfraction of the amount of base glass flowing from the tank 10, theproportion depending upon the composition of the frit, the intensit ofthe color desired in the end product, or other variable factors. Ingeneral, the ratio of base glass to frit usually varies from about 20 to1 to 80 to l or from about 1 percent to about 5 percent by weight offrit glass based on the base glass.

The above-described apparatus is only exemplary of several forms ofapparatus which may be used in practicing the invention, andillustrates, rather schematically, the adoption of the method toexisting forehearth constructions. For another suitable apparatus formixing colorants in the glass furnace forehearth, see US. Pat. No.3,057,175, R. R. Rough et al., issued on Oct. 9, 1962.

THE FRIT GLASS OF INVENTION AND METHOD OF PREPARATION TABLE I.-BA'ICHDATA FOR FRIT GLASSES TABLE II.COMPOSITIONAL DATA FOR FRIT GLASSES INPERCENT BY WEIGHT Example Theoretical chemical Operable analysis I IIIII range TABLE III.-ACTUAL COMPOSITION OF COLORANTS IN FRIT GLASSES INPERCENT BY WEIGHT In one specific embodiment of the present invention,the batch ingredients listed in the corresponding column of Table I arefired in a frit furnace at a melting temperature of about 2750 F. Toproduce the proper ratio of Cr O /CrO the melting fires were slightlyoxidizing. The molten colorant glass is suitably converted to powderedfrit by feeding as a stream from the outlet of the melting furnace andchilling rapidly. The chilling is effected by flowing the molten streamthrough water-cooled rolls and then into a body of water so that theglass breaks up into granular frit form. If desired, the granular glassfrit can then be further reduced in particle size by grinding. We havefound that powdered frit glass particles in the range of from 8 to +30mesh size are satisfactory for the purposes of this invention.

As an alternate method, the frit may be melted and directly fed into theforehearth as the molten colorant glass.

In any event, the theoretical composition of the frit glass based on theabove-mentioned batch charge is listed in the corresponding column ofTable II. The ratio of the essential colorants is set forth in TableIII.

Example II The corresponding frit glass of Table I is prepared accordingto the method of Example I. Compositional data is set forth in Table IIand Table III.

Example III The corresponding frit glass of Table I is preparedaccording to the method of Example I. Compositional data is set forth inTable II and Table III.

USE OF FRIT GLASSES Before describing the manner in which the frits ofthis invention are incorporated into colorless base glasses to producehigh color composite blue glasses, a description of suitable baseglasses and desired composite glass optical properties will be providedto serve as an appropriate background upon which the invention can besuperimposed.

THE PREPARATION OF BASE GLASSES Base glasses that can be used inpracticing the present invention may have an actual analysis of oxidesencompassed within the ranges set out below. Generally, it will be foundthat glasses falling within these ranges are sodalime-flint glassescommonly used in the manufacture of colorless containers.

RANGE OF OXIDES IN BASE GLASS COMPOSITIONS Constituent: Percent byweight SiO 60-75 A1 0.3- CaO+MgO 6-15 Na O 12-18 K 0 0-5 BaO 0-5Decolorizers Trace 1 Any compatible deeolorizer can be used. Thefunction here is to mask the color produced by any iron that may bepresent as an impurity in the batch material. We have found thatselenium in the range of 0.00025-0.00035% is effective.

TABLE IV.--SPECIFIC COMPOSITION OF A SUIT- ABLE BASE GLASS Constituent:Percent by weight Si0 72.08 A1 0 1.70 F3203 CaO 1 1.59 MgO 1.00 N320 .35K 0 0.20 Selenium 0.00025-0.00035 DESCRIPTION OF OPTICAL PROPERTIES Theoptical properties hereinafter set forth are C.I.E. colorimetric valuesbased upon the I.C.I. Chromaticity Diagram. C.I.E. refers to the FirstInternational Commission of Illumination and the diagram from which thevalues are taken defines color in terms of mixtures of theoretical colorlights. The C.I.E. system makes possible the exact specification ofcolors by means of a color map. The C.I.E. system of color notationspecifies the color of glasses in terms of brightness, purity anddominant wavelength.

Brightness which is usually expressed in terms of percentage is theamount of visual response to a normal observer to the radiation emergentfrom a transparent object relative to the response in this observer tothe radiation incident upon this object. Thus, brightness may be brieflytermed the lightness of color of an object.

Purity, which is also normally expressed in terms of percentage, is ameasure of the monochromaticness of a color with monochromatic lighthaving a purity of 100%. By diluting the monochromatic radiation withwhite light made up of all wavelengths, we thereby dilute the color andreduce purity.

Dominant Wave Length, usually expressed in millimicrons (m is thewavelength of monochromatic light appearing to the eye to have the samehue as the mixed light actually encountered. These concepts will behereinafter discussed in relation to the finished composite glass.

COMPOSITE GLASS PRODUCTION In the production of glass containers, a baseglass is prepared in melting tanks of several hundred tons capac ity.The batch constituents are added and proceed through the tank undermelting and refining conditions. The glass is issued out of the firedend of the melting tank by being run through one or a plurality offorehearths which are provided in connection with the tank to feedcontainer forming machines.

Generally, the colorless base glass issues from the melting tank intothe forehearth at a temperature of about 2300 F. The frits made inaccordance with the present invention are well adapted for addition tothe base glass at such temperature conditions in finely divided form asfrom 8 to +30 mesh size. Stirring means and mixing baffles known in theart are used to produce homogeneous admixtures of the frit into thecolorless base glass to produce a uniformly highly colored compositeglass. A specific type of forehearth equipped with stirring is set forthin aforesaid FIG. 1.

Example IV To produce a deep blue composite glass that exhibitsexcellent ultraviolet radiation protection, the frit of Example III wasadded to the forehearth of a furnace producing the base glass listed inTable IV at the rate of about 67 lb. of frit glass per ton of baseglass. In practice, the amount of frit glass usually ranges from about40 to about lb./ ton of base glass. The mixing was accomplished in anapparatus similar to that shown in FIG. 1. The frit was at ambienttemperature and the base glass was about 2300 F. The blue compositeglass was then formed into glass containers by conventional formingequipment.

The composite glass so produced had the following characteristics:

Percent by weight Dominant wavelength (millimicrons), 466.82 460-475Purity, 88.58% 80-90 Brightness, 0.24% 0.2-O.6

Optical measurements refer to 10 mm. thickness sample.

For reference purpose, the data for the standard Maryland Blue Glass forthe same 10 mm. thickness is given:

Dominant wavelength (millimicrons) 445 Purity, percent Brightness,percent 0.70

Complete color profiles for the above glasses are given in FIG. 2. Thisdrawing clearly demonstrates the desirable short-wave absorptionproperties of a deep blue glass composition attainable through thepractices in and teachings of the present invention in comparison withthose of standard Maryland Blue Glass.

Frit glass and base glass Table 11-3 and Table Preferred IV rangeConstituent of composite glass It is evident from the foregoing that thepresent invention provides: 1) new, optically desirable blue glass thatexhibits exceptional absorption in the short-wave visible andultraviolet radiation range, (2) a convenient economical method ofpreparing said blue glass by the addition of a highly colored frit glassto the forehearth of a furnace producing ordinary colorless soda-limeglass.

While the preferred embodiments have been described above in detail, itwill be understood that numerous modifications might be resorted towithout departing from the spirit and scope of the invention. 1

What is claimed is:

1. In a method of making a blue, ultraviolet absorbent, soda-lime glass,the steps of preparing a molten colorless, soda-lime base glass, flowingthe molten base glass through a forehearth, dissolving in the moltenglass in the forehearth a highly enriched colorant frit consistingessentially of a soda-lime flint glass composition containing from about1.5 to about 2.2% total chromium calculated as Cr O from about 0.3 toabout 0.6% CrO calculated as CrO said recited range amount of Cr O insaid frit being adjusted to accommodate the amount of CIO;;, and fromabout 2.2 to about 3.0% C00 and forming a composite blue glass, theamount of said colorant frit dissolved in said base glass ranging from1% t0 5% by weight of the molten base glass.

2. In a method of making a colored glass composition, the steps ofpreparing a substantially colorless molten base glass having thefollowing composition:

Ingredients: Parts Sand 2000 Soda ash 1151-1172 Limestone 557-559Potassium dichromate 98-135 Black cobalt oxide 81-102 dissolving saidfrit in said molten glass under exposure to temperature and oxidizingconditions yielding a final colored glass composition containing fromabout 0.03 to about 0.06% total chromium calculated as Cr O 0.003 to0.01% CrO and 0.03 to 0.1% C00 and said final glass composition havingC.I.E. colorimetric values for millimeter thickness of about 0.2 to 0.6%brightness, 80 to 90% purity, and 460 to 475 millimicrons dominantwavelength.

8 3. A frit composition comprising a soda-lime flint glass which ishighly colorant enriched and which consists essentially of the followingingredients in the indicated percentages by weight:

Ingredient: Percent by Weight SiO 60-65 A1 0 (1.0 -0.1 Fe O 0.0-0.05 CaO8.5-9.5 MgO 0.0-1.0 Na o 18.0-23.0 K 0 0.0-2.0 Total Cr as Cr O 11.5-2.2 C1O 0.3-0.6 CoO 2.2-3.0

1 The amount of CIgOS being adjusted to accommodate the amount of CrOs.

4. A frit composition as described in claim 3, wherein the specificcomposition is:

5. A frit composition as described in claim 3, wherein the specificcomposition is:

Ingredient: Percent by weight SiO 63.46 A1 0 0.07 F203 CaO 9.13 MgO 0.67Na O 21.61 K 0 1.01 Total Cr calculated as Cr O 1 1.61 C00 2.42

1 A proportion of said Cr being present as CIOa calculated as ClOa andconsisting of 0.50 percent by Weight.

6. A frit composition as described in claim 3, wherein the specificcomposition is:

Ingredient: Percent by weight SiO 62.70 A1 0 0.07 Fe O CaO 9.00 MgO 0.67Na O 20.9'8 K 0 1.37 Total Cr calculated as Cr O 1 2.2 C00 2.99

An amount of said Cr 0s being present as CrOs, said amount being about0.6 calculated as CrOs percent by weight.

7. The method as claimed in claim 1, wherein said highly enrichedcolorant frit is in finely divided form.

8. The method as claimed in claim 7, wherein said frit in finely dividedform measures from -8 to +30 mesh size.

References Cited UNITED STATES PATENTS 3,291,621 12/1966 Hagedorn 106-522,923,636 2/1960 Swain 10652 3,330,638 7/1967 Brown 106-54 HELEN M.MCCARTHY, Primary Examiner U.S. Cl. X.R. 106-48, 52

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 779Dated August 11, 1970 Inventor(s) H. R. Keshari and W. F. Mahoney It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

Column 1, line 20 after "soda-lime" insert -glass. Column 2 line 21,"utlizing" should be -utilizing. Column 3, line 48 b "31" should be---].3--.

Signed and sealed this 0th day of June 1975.

SEAL) t Attes c. MARSHALL DANN RUTH C. MASON Commissioner of PatentsAttesting Officer and Trademarks

